stackNqueues.java

class Solution {
    
    HashMap<Character, Character> mappings;
    
    public Solution() {
        this.mappings = new HashMap<Character, Character>();
         this.mappings.put(')', '(');
            this.mappings.put('}', '{');
            this.mappings.put(']', '[');
    }
    
    public boolean isValid(String s) {
        
        Stack <Character> stack = new Stack<>():
        
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            
            if (c == '(' || c == '{' || c == '[') {
                stack.push(c);
            }
            else if (c == '}' && !stack.isEmpty() && stack.peek() == '{') {
                stack.pop();
            }
             else if (c == ']' && !stack.isEmpty() && stack.peek() == '[') {
                stack.pop();
            }
        }
        return stack.isEmpty();
    }
}